1. Field of the Invention
The present invention relates to multi-purpose catheters and in particular, to multi-purpose multi-parameter cardiac catheters having multiple lumens and useable separately to perform diverse independent procedures including oximetry, thermal dilution and continuous cardiac output to obtain significantly useful blood parameters, such as oxygen saturation values (SvO.sub.2), thermal dilution values and continuous cardiac output values.
2. History of the Prior Art
Multi-lumen cardiac catheters are known. Further, it is known to provide within a multi-lumen catheter a plurality of optical fibers, such optical fibers used in conjunction with a signal processing apparatus to measure the oxygen concentration (SVO.sub.2) in the blood.
Thermal dilution catheters have been provided for the measurement of the temperature of mixed fluids in the blood and veins in order to provide important diagnostic information. Exemplary of the patent art relating to such catheters is the patent of H. Khalil, U.S. Pat. No. 4,217,910 and the patents and literature referred to therein.
Thermal dilution is the application of the calorimetric principle that, in a mixture of fluids of different temperatures, the heat lost by one fluid equals the heat gained by the other. For each fluid the mathematical product of the temperature change, specific heat and mass is equal.
The recognized method for the study of blood circulation involves producing a temperature change in the blood at one point in the blood flow and measuring the temperatures change at a second point downstream of the first one. Assuming that the measurement of the temperature change occurs at a point downstream of the heat source, and that the heat content of the blood is uniform, the measured change will reflect the amount of blood passing through the blood vessel. Thus, thermal dilution techniques can provide an intermittent measure of cardiac output.
It is also known to provide an injectateless method of measuring cardiac output in which a small heater or cooler is incorporated into the catheter to generate a temperature change which is measured downstream of the heat source, in a manner similar to the introduction of an injectate into the blood stream through the thermal dilution method, such injectateless method to provide a continuous measure of cardiac output.
Each technique described above provides an important function in determining certain critical parameters associated with the treatment of a critically ill patient. However, the methods described to obtain such parameters are diverse, not necessarily compatible, and to date, unable to be obtained through the use of a single cardiac catheter device.
However, it would be desirable to combine within a single catheter the diverse mechanisms required to monitor not only the oxygen concentration in the blood, but also continuous cardiac output and further to provide within the same catheter a method for conducting thermal dilution measurements.